Jeremiah Cornelius writes: A letter signed by five professors from the University of California, San Francisco and Arizona State University challenge claims made for the safety of the backscatter X Ray scanners, in use by TSA: "The document is heavily redacted with red stamps over the words and figures. In every case the electric current used which correlates one to one with X-ray dose has been specifically redacted. Thus there is no way to repeat any of these measurements... In fact the JHU APL personnel,..were not provided with a machine by Rapiscan. Instead they were invited to the manufacturing site to observe a mock-up of components (spare parts) that were said to be similar to those that are parts of the Rapiscan system."